Systems and methods for managing and utilizing excess corn residue

ABSTRACT

Systems and methods for managing excess above-ground corn residue are disclosed. Systems and methods for combusting corn residue to produce heat for generating steam are also disclosed. Additionally, methods and systems for harvesting and pre-processing corn residue prior to combustion of the corn residue are disclosed.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 14/249,114,filed Apr. 9, 2014, which is a divisional of application Ser. No.12/946,474, filed Nov. 15, 2010, now U.S. Pat. No. 8,712,787, whichapplications are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates generally to systems and methods forusing biomass as fuel for generating power.

BACKGROUND

Above-ground corn residue (i.e., corn stover) typically is considered toinclude the corn stalks, leaves, husks and cobs remaining in the fieldafter the corn grain (i.e., the kernels of grain) has been harvested. Inaccordance with traditional agricultural practices, many corn growerschoose to leave above-ground corn residue on their fields for thepurpose of maintaining soil fertility and organic content. Corn growersthat also raise cattle often use corn residue as a feed source for thecattle. For example, the corn residue can be grazed as forage, or baledand used as fodder or bedding. Corn residue has also been considered foruse in the production of cellulosic ethanol and has further beenconsidered for use as a fuel source that can be co-fired with coal incoal fired burners where coal is the primary fuel.

SUMMARY

One aspect of the present disclosure relates generally to systems andmethods for assisting high yield corn growers in their effort toeffectively manage excess corn residue while concurrently generatingpower from the excess corn residue.

Another aspect of the present disclosure relates to systems and methodsfor effectively harvesting and baling corn residue, and for effectivelyusing such harvested corn residue as a primary fuel source in a steamgeneration facility.

Examples representative of a variety of inventive aspects are set forthin the description that follows. The inventive aspects relate toindividual features as well as combinations of features. It is to beunderstood that both the foregoing general description and the followingdetailed description merely provide examples of how the inventiveaspects may be put into practice, and are not intended to limit thebroad spirit and scope of the inventive aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating a method for managing excess cornresidue and for using the corn residue to generate steam in accordancewith the principles of the present disclosure;

FIG. 2 shows an example site location for a corn residue combustion andsteam generation facility in accordance with the principles of thepresent disclosure;

FIG. 3 is a diagrammatic plan view of a site layout for a corn residuecombustion and steam generation facility in accordance with theprinciples of the present disclosure;

FIG. 4 shows a first shredder/windrower in the process of performing acorn residue windrowing operation in accordance with the principles ofthe present disclosure;

FIG. 4A shows a second shredder/windrower suitable for windrowing cornresidue in accordance with the principles of the present disclosure;

FIG. 4B shows a third shredder/windrower suitable for windrowing cornresidue in accordance with the principles of the present disclosure;

FIG. 4C shows a fourth shredder/windrower suitable for windrowing cornresidue in accordance with the principles of the present disclosure;

FIG. 4D shows a fifth shredder/windrower suitable for windrowing cornresidue in accordance with the principles of the present disclosure;

FIG. 5 shows a baler in the process of conducting a corn residue balingoperating in accordance with the principles of the present disclosure;

FIG. 5A is a side view of a portion of the baler of FIG. 5;

FIG. 6 shows an accumulator for collecting bales from a field;

FIG. 7 is a flow chart showing a method for utilizing corn residue inaccordance with the principles of the present disclosure;

FIG. 8 is a diagrammatic plan view of a pre-processing station of thesite layout of FIG. 3;

FIG. 9 is a diagrammatic side view of a material reducing machine housedat the pre-processing station of FIG. 8;

FIG. 10 is a diagrammatic plan view of a reclamation station of the sitelayout of FIG. 3;

FIG. 11 is a diagrammatic side view of the reclamation station of FIG.10;

FIG. 12 is a diagrammatic plan view of an alternative configuration forthe reclamation station of the site layout of FIG. 3;

FIG. 13 is a diagrammatic side view of the reclamation station of FIG.12; and

FIG. 14 is a schematic view of a combustion and steam generation stationand an electricity generation station of the site layout of FIG. 3.

DETAILED DESCRIPTION

Traditionally, corn growers have managed their corn residue by tillingthe corn residue into the soil after the grain has been harvested.Traditional wisdom teaches that tilling the corn residue back into thesoil is necessary to maintain the nutrient value and organic content ofthe soil. Thus, it has generally been believed that tilling the cornresidue back into the soil helps the soil support increased yields andreduces the amount of artificial fertilizers and soil conditioners thatneed to be applied to the fields.

The total biomass of a corn plant includes the corn grain, theabove-ground corn residue, and the underground root system. Generally,the corn grain represents about one-third of the total biomass of a cornplant, the above-ground corn residue represents another one-third of thetotal biomass of the corn plant and the root system represents the finalone-third of the total biomass of the corn plant. A bushel of corn graincan be assumed to weigh about 56 pounds. This being the case, for eachbushel of corn grain, 56 pounds of above-ground corn residue is alsoproduced.

Advancements in farming technology have resulted in significantlyincreased corn grain yields per acre. With ever increasing corn grainyields, the total amount of corn residue per acre has also increased.Increased levels of corn residue have presented problems for today'sfarmers. For example, high levels of corn residue can jam or clogtillage equipment thereby preventing the corn residue from beingeffectively plowed back into the field. Moreover, the soil cannotreadily accept and decompose the large amounts of corn residue thatresults from today's increased corn yields. As a result, corn residue isnot uniformly integrated and broken down into the soil which can resultin slow or uneven field warming. Also, excessive amounts of corn residuein the soil can delay germination due to slower water absorption causedby inadequate soil to seed contact. Moreover, chemicals leaching fromcrop residue can delay early crop growth. The above problems associatedwith excessive corn residue can interfere with a corn grower's abilityto maximize yields. Therefore, for high-yield corn crops, it is believedthat removing a significant portion of the excess corn residue from thecorn grower's fields will result in higher yields without negativelyimpacting the long term productivity of the soil. For example, researchhas shown that under certain conditions, removing about half of theabove-ground corn residue from the field can provide as much as a 13bushel per acre increase in the corn grain yield which also results inapproximately an additional 728 pounds per acre of extra above-groundcorn residue.

The present disclosure relates to methods and systems that can help corngrowers effectively solve their excess corn residue problems whileconcurrently being compensated for their excess corn residue. Thepresent disclosure also provides methods and systems that benefit thecommunity at large by providing power from a bio-renewable fuel sourcewhile simultaneously creating local jobs.

FIG. 1 is a flow chart illustrating a wide-scale method for managing andutilizing excess above-ground corn residue in accordance with theprinciples of the present disclosure. The method starts with a firststep 10 where a particular facility site location is identified. Anumber of factors should be considered when identifying an appropriatesite location. For example, a suitable site location should be in closeproximity to a high density of high-yield, corn-on-corn acres. As usedherein, the term “high-yield” corn acres means corn acres providing agrain yield of at least 180 bushels of corn grain per acre. Corn-on-cornacres are acres where corn is repeatedly planted in successive years. Itis preferred for there to be at least 880,000 acres of high-yield,corn-on-corn acres within a service area of the selected site location.Referring to FIG. 2, a site location 12 is shown within a service area14 having a 30 mile radius in which 880,000 acres of high-yieldcorn-on-corn acres are located. In a most preferred embodiment, the880,000 acres of high-yield corn within the service area 14 provide anaverage grain yield of at least 190 bushels of corn grain per acre. Itis believed that utilizing 50 percent of the above-ground corn residuepresent on 4 percent of the 880,000 acres of high yield corn within theservice area will provide a source of biomass fuel that is sufficientlylarge to allow the facility to operate continuously for one year. Thisrepresents about at least 174,000 tons of corn residue based bio-fuelper year. By building the site location 12 in close proximity to a largeamount of high-yield corn, the site location 12 is positioned in closeproximity to a large source of bio-fuel in the form of excess cornresidue. The close proximity of the bio-fuel allows bio-fueltransportation costs to be minimized thereby enhancing the costeffectiveness of the overall system.

It is also significant for the site location 12 to be in close proximityto a market having a stable demand for electricity. This generally meansthat the site location is relatively close to larger population centerswhich provide a stable demand for electricity thereby keeping the priceof electricity stable. In certain embodiments, the site location 12 ischosen so that electricity generated at the site location 12 can be soldon the PJM market or a like market for electricity.

Once a site location has been identified, the second step 20 of themethod of FIG. 1 includes constructing a combustion and steam generationfacility 13 (see FIG. 3) at the site location 12 for pre-processing andcombusting excess corn residue harvested/collected from the service area14. The facility 13 can include a combustion and steam generationstation 15. The combustion and steam generation station 15 can bereferred to as a combustion and steam generation unit, island,arrangement, or like terms. The combustion and steam generation station15 can include a furnace for combusting corn residue and a boiler thatuses combustion heat from the furnace to generate steam. The facilitycan also include a steam turbine generator 17 (i.e., a steam turbinethat cooperates with an electrical generator) to convert heat energyfrom the steam into electrical energy. Alternatively, the steam could beused for other applications. For example, the steam could be used in acellulosic or grain ethanol production process or other processes usingprocess steam.

It is preferred for the furnace of the combustion and steam generationstation 15 to be configured to combust corn residue as a primary fuel.Of course, the furnace can include a source of supplemental heat such asnatural gas burners that would typically be used at furnace start-up andshut-down operations. However, it is preferred for corn residue to bethe primary (i.e., the main fuel) fuel burned in the furnace duringnormal operations between start-up and shut-down. In certainembodiments, corn stover is the only fuel burned in the furnace forcertain periods of time. In other embodiments, a mixture including cornstover as a primary component and another fuel source (e.g., waste seed)as a secondary component can be burned in the furnace.

The facility 13 further can further include a pre-processing station 19including a storage lay-out for providing storage of some of theharvested corn residue on site. In certain embodiments, the storagelay-out can include a short-term staging area 21 within a pre-processingbuilding for holding the corn residue immediately before pre-processing,and an outside back-up storage area 23 for storing a back-up supply ofcorn residue (e.g., a one week supply of corn residue which typicallywould constitute at least 3400 bales that each weigh 1250 pounds). Theback-up supply ensures that the facility 13 can continue to operate fora predetermined period of time in the event that weather or otherfactors interfere with the continuous supply of corn residue to thefacility. The pre-processing station 19 can include processing equipment27 within the pre-processing building for pre-processing (e.g.,shredding) the corn residue prior to combustion.

Referring still to FIG. 3, the facility 13 can include a reclamationstation 25 that provides a buffer between the pre-processing station 19and the combustion and steam generation station 15 for staging thepre-processed corn residue in an enclosed space for a limited time priorto feeding the pre-processed corn residue into the furnace of thecombustion and steam generation station 15. The reclamation station 25allows the pre-processing station 19 to be operated for set durations oftime per day (e.g., 8-10 hours) while the combustion and steamgeneration station 15 is operated continuously. When the pre-processingstation is operated, the rate at which the pre-processed corn residue isproduced exceeds the rate at which the combustion and steam generationstation 15 consumes the corn residue. Thus, the excess pre-processedcorn residue generated by the pre-processing station 19 is stock-piledat the reclamation station 25. The amount of corn residue stock-piled atthe reclamation station 25 is sufficient for the combustion and steamgeneration station 15 to operate continuously over the time period inwhich the pre-processing station 19 is shut-down.

The facility 13 preferably further includes pollution abatementequipment. For example, the facility 13 can include equipment (e.g.,mechanical filters, mechanical separators such as cyclonic separators,precipitators, or other structures) for removing particulate materialsuch as fly ash from the exhaust stream generated by the facility. Thefacility can also include a selective non-catalytic reduction (SNCR)system to reduce the concentration of nitrogen oxides (NO_(x)) in theexhaust emissions. Further, the facility can also include an acid gascontrol system for neutralizing acid gases present in the exhaustemissions.

Referring back to FIG. 1, the third step 30 of the depicted methodinvolves contracting with corn growers in the service area 14 to harvestexcess corn residue on their behalf. Typically, the facility operatorwill enter into multi-year contracts (e.g., three year, five year, etc.)with the corn growers with regard to harvesting of the excessabove-ground corn residue. The amount of corn residue harvested may varyfrom corn grower to corn grower. For example, some corn growers maycontract to have all of the corn residue on a given acreage harvestedand removed from the field by the facility operator. However, many ofthe corn growers in the service area may elect to have only a portion oftheir corn residue harvested and removed from the field. The amount ofcorn residue that can be harvested is typically dependent upon the yieldof the corn crop at issue. For high-yield corn acreages having a yieldequal to 180 bushels per acre or more, it is preferred for the contractto specify that at least 50% of the above-ground corn residue can beharvested by the facility operator. In typical applications, 40% to 60%of the corn residue can be sustainably harvested without reducing soilproductivity. This being the case, depending upon the yields of the corncrop at issue, the amount of corn residue contracted to be harvestedcould typically be in the range of 2.25-2.5 tons per acre.

It will be appreciated that the time period for harvesting the cornresidue is rather short and limited generally to one to two months. Thisbeing the case, it is preferred for the contract to require the corngrower to notify the facility operator when the corn grower intends toharvest the grain and when the grower has actually harvested the grain.Also, the contract can require the corn grower to provide the facilityoperator with information relating to the corn crop (e.g., currentmoisture content of the corn grain, current moisture content of the cornstover). The above information allows the facility operator toefficiently plan when the above-ground corn residue can be harvested.The contract may also require the corn grower to make available apredetermined amount of the corn grower's acreage for storage of theharvested corn residue by the facility operator. The time periodspecified for storage of the harvested corn residue on the corn grower'sproperty may range from 1 to 12 months.

At the fourth step 40 of the method of FIG. 1, the facility operatorharvests the excess corn residue on the corn grower's behalf. It ispreferred for the corn residue to have a moisture content in the rangeof about 10-15 percent at the time the corn residue is harvested. Themoisture content of the corn residue affects the efficiency at which thecorn residue is combusted. If the corn residue is too moist, the BritishThermal Unit (BTU) value of the corn residue drops. In contrast, energytransfer rates reduce if the corn residue is too dry. Therefore, it isoften desirable for the excess corn residue to remain in the field for apredetermined amount of time after the grain has been harvested beforethe excess corn residue is harvested. In this way, the excess cornresidue is allowed to dry to the desired level in the field due to theeffects of wind, sun, and low relative humidity. Once the corn residuereaches the desired moisture content, the corn residue is harvested.

The initial moisture content data provided to the facilitator operatorby the corn grower at the time the grain is harvested can provide arough estimate as to how long the excess corn residue should remaindrying in the field prior to being harvested. Moisture testing can beconducted to anticipate/predict the appropriate time at which the cornresidue can be harvested. The corn residue can be tested for moisturecontent by inserting moisture testing probes at a plurality of locationsalong the lengths of a plurality of stalks, and then averaging theresults. Alternatively, a number of pieces of residue (e.g., stalk,leaves, cobs) can be reduced in size (e.g., shredded) and placed in apile, and the moisture testing probes can be used to determine themoisture content at different locations within the pile. The differentmoisture readings taken for the pile can be averaged to determine theoverall moisture content of the corn residue.

It will be appreciated that a significant amount of harvesting will needto be completed by the facility operator in a relatively short amount oftime. To accomplish this harvesting, harvesting equipment, (e.g.,shredders, windrowers, balers, accumulators) can be short term leased bythe facility operator. Also, third parties can be hired as independentcontractors working under the supervision of the facility operator forconducting the corn residue harvesting operations.

Once the corn residue in the contracted corn grower's field dries to thedesired moisture content, the corn residue can be harvested by thefacility operator. At shown at FIG. 4, the harvesting process canutilize a shredder/windrower 250 pulled by a tractor 252. Theshredder/windrower 250 has a main housing 251 having a length thatextends between first and second ends 247, 249. The shredder/windrower250 defines a centerline 257 that bisects the housing 251 and isperpendicular to the length of the housing 251. The centerline 257extends generally along a direction of travel of the shredder/windrower250. The shredder/windrower 250 has a discharge chute 253 positioned atthe first end 247 of the housing 251. The end positioning of the chute253 allows two passes across a given field to be piled into a singlewindrow 255 (i.e., a combined windrow). The shredder/windrower 250 caninclude a cutting mechanism such as cup cutters 256 (i.e., cup knives)mounted on a rotating carrier 258 such as a drum or shaft rotatableabout an axis of rotation 260. The cutting mechanism is mounted withinthe housing 251. The shredder/windrower 250 can also include across-conveyor such as a cross auger 262 mounted within the housing 251for conveying corn residue cut by the cup cutters 256 laterally alongthe length of the housing 251 to the end discharge chute 253. One ormore paddles 255 can be mounted on the carrier 258 for discharging thecorn residue rearwardly out the discharge chute 253. Theshredding/windrowing operation preferably is undertaken when themoisture content of the corn residue is in the range 10-15 percent.

For baling purposes, it is desirable for the combined windrow to have awidth w less than about 42 inches and a fairly constant/uniform heightacross the width of the combined windrow. To achieve such a combinedwindrow, it is desirable for the corn residue collected from the secondpass across the field to be piled at least partially on top of thewindrow from the first pass. Preferably, this is accomplished withoutriding over a portion of the first windrow which can cause balling andoverall disruption of the windrow. To allow the second windrow to bepiled over the first windrow, it is desirable for the discharge chute253 to be adjustable to cause the corn residue to be discharged at leastpartially in a lateral direction outwardly from the first end 247 of thehousing 251. In certain embodiments, the first windrow can be depositeddirectly behind the shredder/windrower and the second windrow can bedischarged from the chute in a direction extending at least partiallylaterally outwardly from one end of the shredder/windrower so that thesecond windrow can be piled at least partially over the first windrow.

FIGS. 4A-4D show various configurations for adjusting the dischargestream directed from a shredder/windrower. FIG. 4A shows ashredder/windrower 250 a having a discharge chute 253 a including innerand outer guides 264, 265 that can be pivoted about vertical axes 266,267 relative to respective inner and outer walls 268, 269 of the chute253 a. Once pivoted to a desired position, the guides 264, 265 can besecured in place (e.g., with fasteners, clamps, etc.). The guides 264,265 can be oriented parallel to the centerline 257 or angled relative tothe centerline 257. When the guides 264, 265 are angled away from thecenterline 257, material discharged from the chute 253 a moves in adirection angled laterally outwardly away from the centerline 257.

FIG. 4B shows a shredder/windrower 250 b having a discharge chute 253 bincluding inner and outer walls 270, 271. A guide 272 is pivotallyattached to the inner wall 270. The guide 272 can be angled relative tothe centerline 257 so that material discharged from the chute 253 bmoves in a direction angled outwardly away from the centerline 257. Theguide 272 can also be oriented so that the chute 253 b dischargesmaterial in a rearward direction parallel to the centerline 157.

FIG. 4C shows a shredder/windrower 250 c having a discharge chute 253 cincluding inner and outer walls 273, 274. A blocking plate 275 isslidably attached to the inner wall 273. The blocking plate 275 canslide along a slide orientation that is transverse relative to thecenterline 257 to vary the discharge area of the chute 253 c. By movingthe blocking plate 275 away from the centerline 257 along the slideorientation and securing the blocking plate 275 in place, the dischargearea of the chute 153 c is made narrower. Also, because the adjustmentis made at the inner wall 273 as compared to the outer wall 274, theoutside edge of the windrow formed from the chute 253 c is moved awayfrom the centerline 257. The smaller width of the chute 253 c openingcombined with the positioning of the outer wall 274 of the chute opening253 c in close proximity to the outer end of the shredder/windrower 250c assists in making a narrower combined windrow because two relativelynarrow windrows can be deposited side-by-side with minimal gapsthereinbetween.

FIG. 4D shows a shredder/windrower 250 d having a discharge chute 253 dincluding inner and outer walls 280, 281. One or both of the walls 280,281 can be moved relative to the main housing of the shredder/windrower150 d to control a direction in which the corn stover is discharged formthe chute 250 d. By moving the walls 280, 281 about vertical pivot axes,the walls 280, 281 can be moved to orientations angled toward thecenterline 257, parallel to the centerline 257 or away from thecenterline 257.

It is desirable for the shredding/windrowing operation to be controlledsuch that the amount of corn residue harvested from a given acreagecorresponds to the contracted amount. To control the amount of residueharvested, the shredder/windrower 250 can be set at different cuttingheights, with lower cutting heights corresponding to more tons of cornresidue harvested per acre and higher cutting heights corresponding tofewer tons of corn residue harvested per acre. In certain embodiments,the cutting heights can range from 2 inches to 20 inches. In preferredembodiments, the cutting heights are in the range of 8 to 15 inches or6-12 inches.

During the harvesting process, it is desirable to minimize the dirt andother debris present in the windrows. Corn growers prefer as much soilas possible to remain in their fields. Also, increased soil content inthe harvested corn residue can dilute the value of the fertilizer thatresults as a by-product from processing the corn residue. Further, theweight attributable to excess dirt in the corn residue increasestransportations costs. Moreover, excess dirt in the corn residue canmake bales made from the corn residue more difficult to handle withequipment such as accumulators since the bales tend to slide lesseasily.

During windrowing, the rotation of the cup cutters 256 creates a vacuumeffect that assists in drawing corn residue and also dirt up into thewindrower 250. In this regard, the amount of dirt collected is dependentupon the height the corn residue is cut during windrowing/shredding.Higher cuts result in less dirt in the windrowed corn residue whilelower cuts result in more dirt in the windrowed corn residue. The amountof dirt in the windrowed corn residue can also be controlled by varyinga tilt angle of a tow bar of the windrower 250.

The amount of vacuum generated by the cup cutters 256 is directlydependent upon the speed at which the cup cutters 256 are rotated aboutthe axis 260. It is therefore desirable to control the rotational speedof the cup cutters so that corn residue is effectively carried to thehorizontal conveyor without also carrying excessive amounts ofdirt/soil. Typically, a tractor power take-off operates at a rotationalspeed ranging between about 900-1100 rotations-per-minute (RPM) and thepower input shaft of the windrower 250 is driven by the power take-offat a 1-to-1 ratio. The power input shaft of the windrower drivesrotation of the rotating carrier 258. Under conditions where excessivedirt collection is an issue (e.g., low cuts, dry conditions), theoperator can operate the tractor so as to minimize the rotational speedof the power take-off. For example, the tractor can be operated suchthat the power take-off speed is less than 1000 RPM or less than 950RPM. By lowering the power take-off speed, the rotational speed of thecup cutters 256 is lowered thereby lowering the vacuum effect of the cupcutters 256

In certain embodiments, a rotation speed adjustment mechanism (e.g., agear box or variable speed transmission) can be used to allow therotational speed of the rotating carrier 158 to be adjusted to match agiven application. The rotation speed adjustment mechanism can beprovided at some point between the power take-off and the rotatingcarrier 158 or can be provided at the tractor to adjust the rotationspeed of the power take-off. In this way, when it is desirable toprovide a low cut in dry conditions, the rotation speed adjustmentmechanism can be used to lower the rotational speed of the rotatingcarrier 158 to a desired level. Also, for high cut applications, therotation speed adjustment mechanism can be used to increase therotational speed of the rotating carrier 158 to a desired level whichmay allow the tractor to be operated at higher ground speeds.

It is desirable for the shredder/windrower 250 to shred the corn residueto an average length having a target range of 3-12 inches. In certainembodiments, the corn residue output from the windrower 150 to thewindrow 255 has been shredded to an average length having a target rangeof 6-9 inches. Shredding the corn residue to a desired length assists insubsequently producing bales having a desired size and degree ofcompaction.

After the shredding and windrowing operation has been completed, thecorn residue in the windrows 255 is preferably baled (see FIG. 5). Inthe baling operation, it is preferred to create rectangular bales 166 soas to facilitate handling and stacking. In preferred embodiments, thebales can be about 3 feet by 4 feet by 8 feet. To encourage watershedding and to minimize handling and transportation costs, it ispreferred for the bales 166 to be relatively dense. In a preferredembodiment, the bales 166 have a compacted density of at least 13 poundsper cubic foot. In certain embodiments, the bales 166 can have a weightin the range of 1,000-1,500 pounds, or a weight in the range of1,100-1,400 pounds, or a weight of about 1,200 to 1,300 pounds. Theabove weights and compaction rates are applicable for bales formed bycorn residue having a moisture content of about 10 percent. In oneembodiment, the bales 166 are held together by at least six wraps ofplastic twine 168 having a tensile strength of at least 450 pounds. Inother embodiments, other sized rectangular bales (e.g., 4×4×8 foot) oreven round bales could be used.

FIG. 5 shows a baler 400 being pulled behind a tractor 402 along one ofthe windrows 255. As shown at FIG. 5, the baler 400 has compacted aportion of a windrow into a plurality of bales 166. The baler includes athroat 404 that is preferably wider than the windrow 255. A rotatablepick-up mechanism 406 is positioned in the throat 404 for picking up thecorn residue and carrying the corn residue to a set of screw conveyors408 which move the corn residue into a central compaction chamber 410.In the compaction chamber 410, the corn residue is compacted into arectangular bale and then wrapped with twine. The finished bale 166 isdischarged out a back of the baler 400.

Referring to FIGS. 5 and 5A, the rotatable pick-up mechanism 406includes a shaft 412 that is rotated about a central axis 414. Aplurality of radial tines 416 (e.g., fingers, wires, members, etc.) arecarried by the shaft 412 about the central axis 414 as the shaft 412 isrotated. The tines 416 are rotated in a direction which causes the cornresidue to be picked-up by the tines 416 and carried over the top of theshaft 412 to the screw conveyors 408. Positioning the pick-up mechanism406 too close to the ground can lead to tine breakage. However, when thepick-up mechanism 406 is elevated, the pick-up mechanism 402 is unableto pick-up a lowermost layer of the corn residue. Leaving a sizablelayer of corn residue in the windrow can be problematic for corn growerspracticing no-till farming since the layer can interfere with effectiveseed planting and germination. Also, leaving corn residue in thewindrows reduces the overall corn residue harvest. To overcome thisproblem, the baler 400 can include an air assist system 420 forassisting the pick-up mechanism 406 in picking up the bottom layer ofcorn residue in a windrow. The air assist system 420 can include an airdirecting arrangement (e.g., one or more air knives, air nozzles, etc.)that directs a stream or streams of air under the pick-up mechanism 406thereby causing the bottommost layer of corn residue in the windrow tobe lifted up by the air into the path of the rotating tines 416 of thepick-up mechanism 406. In this way, the pick-up mechanism 406 can bepositioned elevated above the ground while still being able to pick upthe bottommost layer of corn residue in the windrow 255.

After the baling process has been completed, the bales are collected andstacked at a temporary storage location on the corn grower's field. Thespace corresponding to the temporary storage location may be leased fromthe corn grower for a specified time period as part of the contract withthe corn grower.

The bales can be collected and stacked using an accumulator device. FIG.6 shows an example accumulator 170 including a vehicle 172 supporting anangled bed 174 and a front lift mechanism 176. In use of the accumulator170, the accumulator 170 is driven across the field and the front liftmechanism 176 is used to lift bales over the top of a cab 178 of thevehicle onto the angled bed 174. To pick up a given bale, it is notnecessary to stop movement of the vehicle. Instead, the bale is pickedup on the fly and lifted over the cab 178 to the angled bed 174. Thebale then slides down the angled bed to a stop to provide room foradditional bales. Once a predetermined number of bales has beenaccumulated on the bed 174, the accumulator 170 returns to the temporarystorage location on the corn grower's field where the bales are slid offof the angled bed 174 to the storage location and stacked at the storagelocation.

At the fifth step 50 of the method of FIG. 1, the bales are transportedfrom the temporary storage locations on the corn grower's fields to thecombustion and steam generation facility. Preferably, the bales remainstored on the corn grower's fields until the bales are needed forcombustion at the facility 13. Thus, the bales can be transported fromthe corn grower's fields and immediately/directly delivered to thepre-processing station 19 for pre-processing without any intermediateoff-site storage of the bales. In this way, the amount of time andenergy spent in handling and transporting the bales is minimized. Incases where storage on the corn grower's field is not an option, thebales can be transported to an off-site storage location where the balesare temporarily stored until the bales are needed for combustion at thefacility site.

At the sixth step 60 of the method of FIG. 1, the baled corn residue atthe combustion and steam generation facility 13 is processed to producepower and useful by-products such as ash. FIG. 7 is an outline thatprovides an overview of the sequence of operations that are conducted atthe facility 13. At step 70, the bales are pre-processed (e.g., reducedsuch as by shredding) at the pre-processing station 19. After beingpre-processed at the pre-processing station 19, the pre-processed cornresidue is conveyed to the reclamation station 25 (see step 72) wherethe pre-processed corn residue is piled in a stock-pile. Thereafter, thepre-processed corn residue is conveyed from the reclamation station 19to the combustion and steam generation station 15 and is combusted (seestep 74). The heat from the combustion of the pre-processed corn residueis used to produce steam (see step 76) which is used to generateelectricity (see step 78). A combustion exhaust stream resulting fromcombustion of the corn residue is treated by pollution abatementequipment (see step 80) prior to being discharged to atmosphere. Fly ashin the exhaust stream is collected (see step 82) and sold (see step 84).

FIGS. 8 and 9 show the pre-processing station 19 of FIG. 3 in moredetail. The pre-processing station 19 includes a pre-processing building90 housing one or more reducing machines 92 and the short-term stagingarea 21. The short-term staging area 21 generally provides enough spaceto store 250-350 bales each weighing about 1250 pounds. The reducingmachine 92 includes an in-feed conveyor 93 that feeds the bales into areducing assembly 94. The reducing assembly includes one or morerotatable reducing units 96 (e.g., drums, rotors, shafts) that carry aplurality reducing elements 97 (e.g., teeth, blades, flails, etc.) forbreaking apart the bales and for reducing the average size of the cornresidue components forming the bales. A screen 99 can be provided forcontrolling the size of the pieces of corn residue that exit thematerial reducing machine 92. The screen 99 at least partially surroundsthe rotatable reducing units 96 and forms a reducing chamber in whichthe rotatable reducing units 99 are positioned. In one embodiment, thereducing machine 92 grinds the corn residue forming the bales such thatthe pieces of corn residue exiting the material reducing machine 92 havean average length less than 3 inches. It is also preferred for the cornresidue exiting the grinders to have no more than 25 percent materialthat is less than 0.25 inches in length. The material reducing machine92 deposits the reduced corn residue on a discharge conveyor 100 thatcarries the reduced corn residue to an elevated conveyor 102. Theelevated conveyor 102 carries the reduced corn residue from thepre-processing building 90 to the reclamation station 25.

Referring to FIG. 8, the pre-processing station 19 includes a truckrouting path 104 that extends through the building 90 so that truckscarrying bales from the corn grower's fields can unload the balesdirectly onto the in-feed conveyor 93 or into the short-term stagingarea 21 in the event the in-feed conveyor 93 is full. The truck-routingpath has a straight pass-through configuration through the building 90.A truck scale can be provided at the pre-processing station 19 fordetermining the weight of each truck's load before the bales areunloaded. The weights can be used to determine how much each corn growershould be compensated pursuant to the contract with the facilityoperator.

The back-up storage area 23 of the pre-processing station 19 is dividedbetween two dedicated areas immediately outside the building 90. Asdescribed above, the corn residue is preferably continuously supplied tothe pre-processing station 19 during operation of the pre-processingstation 19 by delivering the baled corn residue to the pre-processingstation 19 directly from the storage locations on the individual corngrower's fields. Therefore, it is anticipated that poor weatherconditions or extremely wet fields may limit access to the corn residueon the corn grower's fields for periods of time. To address this issue,the back-up storage area 23 provides enough on-site storage of cornresidue to allow the facility to continue to operate over the worst-caseanticipated period of time (e.g., 1 week) in which the field stored cornresidue can not be accessed.

As described previously, the reclamation station 25 provides an enclosedlocation for stockpiling the reduced corn residue that is ultimately fedto the combustion and steam generation station 15. In one embodiment,the reclamation station 25 is configured to stage (e.g., stockpile,store, accumulate) at least 1000 tons of reduced corn residue.

FIGS. 10 and 11 show the reclamation station 25 of FIG. 3 in moredetail. Referring to FIG. 10, the reclamation station 25 includes astorage building 110 having a length L and a width W. An elevatedin-feed conveyor 112 extends along the length L of the reclamationbuilding 110 along the ceiling of the reclamation building 110. Thein-feed conveyor 112 receives the reduced corn residue from the elevatedconveyor 102 that extends between the pre-processing station 19 and thereclamation station 25. The in-feed conveyor 112 is used to fill thereclamation storage building 110 along its length. Over-the-pilereclaimers 114 are located at one end of the building 110. Thereclaimers 114 are used to move the reduced corn residue stored withinthe reclamation storage building 110 to an out-feed conveyor 116. Theout-feed conveyor 116 carries the reduced corn residue to a conveyor 130that extends from the reclamation station 25 to the combustion and steamgeneration station 15. As shown at FIG. 11, each reclaimer 114 includesa conveying structure 118 (e.g., a drag chain or belt) oriented in acontinuous loop about a reclaimer boom 120 that pivots about a pivotaxis 122. Each conveying structure 118 is rotated in a direction ofrotation 124 about its corresponding reclaimer boom 120. The reclaimerbooms 120 are movable about the pivot axes 122 between raised, upwardlyangled positions 126, and lowered positions 128 (see in dashed line).

In use, the reclaimers 114 are initially positioned in the raisedpositions 126 above a pile of reduced corn residue stored within thestorage building 110. To unload stored reduced corn residue from thestorage building 110, the reclaimers 114 are pivoted downwardly from theraised position while the conveying structures 118 are rotated in thedirection of rotation 124. As the reclaimers 114 are moved downwardly,the conveying structures 118 engage the pile of corn residue and dragthe corn residue down the pile laterally along the width W of thebuilding 110 to the out-feed conveyor 116. Once the reclaimers 114 reachthe lower positions 128 such that all of the corn residue previouslystored thereinbeneath has been loaded onto the out-feed-conveyor 116,the reclaimers 114 are raised back to the raised position 126 and cornresidue piled at the opposite end of the building is pushed along thelength L of the pre-processing building 210 to the area beneath thereclaimers 114. In certain embodiments, equipment such as a front endloader is used to push the corn residue beneath the claim conveyors 218.Thereafter, the reclaimers 114 can again be pivoted from the raisedposition 126 to the lowered position 128 to unload the corn residuepushed beneath the reclaimers 114.

FIGS. 12 and 13 show an alternative reclamation conveyor arrangement forthe reclamation station 25. The alternative reclamation conveyorarrangement includes two over-the-pile reclaimers 140 that cooperate toextend across the width W of a reclamation storage building 142. Thereclaimers 140 each include a continuous conveying structure 144 thatloops about a boom 146 that pivots about an axis 148. The conveyingstructures 144 are rotated in directions 150, 152 about theircorresponding booms 146. The reclaimers 140 pivot about the axes 148between raised orientations 154 where the reclaimers 140 are angledupwardly and lowered orientations 156 where the reclaimers 140 aregenerally horizontal and adjacent to the floor of the building 142. Anin-feed conveyor arrangement 158 extends along the length L of thebuilding 142 and is mounted adjacent the top of the building 142. Thein-feed conveyor arrangement 158 receives the reduced corn residue fromthe elevated conveyor 102 that extends between the pre-processingstation 19 and the reclamation station 25. Out-feed conveyors 160 extendalong the length L of the building 142 and are located adjacent thepivot axes 148 of the reclaimers 140. The out-feed conveyors 160 carrythe reduced corn residue to a conveyor 130 that extends from thereclamation station 19 to the combustion and steam generation station15. In certain embodiments, the reclaimers 140 can be mounted on a track162 or other structure that allows the reclaimed conveyors to travel(e.g., to be indexed) along the length L of the building 142.

In operation of the reclamation building 142, the building 142 isinitially filled with reduced corn residue via the elevated in-feedconveyor arrangement 158. To unload corn residue piled beneath thereclaimers 140, the reclaimers 140 are pivoted downwardly from theraised orientations 154 while the conveying structures 144 are rotatedin directions 150, 152 about their respective booms 146. As thereclaimers 140 are lowered, the conveying structures 144 contact thecorn residue piled beneath the reclaimers 140 causing corn residue to bedragged downwardly and laterally across the width of the building 142toward the out-feed conveyors 160. As the reclaimers 140 are graduallymoved downwardly, the material beneath the reclaimers 140 is conveyed tothe out-feed conveyors 160 at the sides of the building 142. Once thereclaimers 140 reach the lower orientations 156, the reclaimers 140 areraised back to the raised orientations 154 and then are indexed orotherwise moved by a transport drive arrangement along the tracks 162 toa position where the reclaimers 140 are oriented above reduced cornresidue that had been previously loaded into the building 142 by thein-feed conveyor arrangement 158. The reclaimers 140 are then lowered tomove the next batch of reduced corn residue to the out-feed conveyors160. It will be appreciated that the above indexing and unload sequencecan be repeated to progressively move the reclaimers 140 along theentire length L of the reclamation building 142. In this way, the entirestorage region of the building 142 can be unloaded without requiringmovement of the stored corn residue within the building 142 bysupplemental equipment such as a front end loader.

FIG. 14 shows the combustion and steam generation station 15 of FIG. 3and the steam turbine generator 17 of FIG. 3 in more detail. Thecombustion and steam generation station 15 includes a furnace 300 wherecorn residue is combusted to produce combustion heat used for generatingsteam at a boiler 302. Steam from the boiler 302 drives a steam turbine303 of the steam turbine generator 17. The turbine 303 powers anelectrical generator 305 which produces electricity that can be sold. Asubstation 315 is used to step-up the voltage of the electricitygenerated by the generator 305 before the electricity is sold.

The furnace 300 of the combustion and steam generation station 15 caninclude a stoker including a vibrating grate 304 on which the cornresidue desired to be combusted is distributed. Combustion air can bedirected into the furnace 300 at a location 311 beneath the grate 304such that the combustion air flows upwardly through the grate 304 duringcombustion of the corn residue. A fan 307 can be used to draw warmedcombustion air from a building 309 housing the furnace 300 to utilizewaste heat generated by the furnace 300. The combustion air can also bepre-heated by a heat exchanger 310 through which exhaust gas from thefurnace 300 passes. The vibrating grate 304 of the stoker can be slopedand is vibrated for auto cleaning. Ash generated by the combustion ofcorn residue is discharged from a discharge end of the stoker grate 304to an ash hopper 306. A conveyor discharges the ash from the hopper to adisposal container 308.

An upper combustion region/volume 312 is provided above the stoker grate304 for combusting suspended fuel particles and combustible gases.Air/gas can be injected into the upper combustion region 312 at nozzles314. The air/gas can be in the form of ambient air or re-circulatedexhaust from the furnace 300 or combinations thereof. Fans 316, 318 canbe used to move the ambient air and/or the re-circulated exhaust.

The corn residue can be delivered to the grate 304 by a fueldistribution system 320 that receives reduced corn residue from a fuelmetering arrangement 322. The fuel metering arrangement 322 receives thecorn residue from the conveyor 130 that extends from the reclamationstation 25 to the combustion and steam generation station 15. The fuelmetering arrangement feeds the corn residue down chutes to the fueldistribution system 320. The fuel distribution system 320 can include apneumatic system that uses a stream of gas/air to carry/blow the cornresidue across the top of the grate 304. The gas/air for the fueldistribution system 320 can be provided by a fuel distributor air fan324 that delivers ambient air to the furnace 300, or by a flue gasrecirculation fan 326 that re-circulates furnace exhaust gas back to thefurnace 300. It will be appreciated that the air/gas sources can be usedalone or in combination. The corn stover fuel fed into the furnacepreferably is a mixture of corn stover pieces having a compositionincluding an average piece length less than 3 inches with no more than25 percent by weight being less than 0.25 inches in length. In oneembodiment, the corn stover fuel fed into the furnace is a mixture ofcorn stover pieces having a composition including at least 75 percent byweight that is less than 3 inches in length and no more than 25 percentby weight that is less than 0.25 inches in length.

Injecting the re-circulated exhaust gas back into the furnace 300, asdescribed above, can assist in controlling NO_(x) emissions. The systemcan also include a NO_(x) removal station 354 for treating the furnaceexhaust. The NO_(x) removal station can utilize anhydrous ammonia toreduce NO_(x) to nitrogen and water.

The boiler 302 of the combustion and steam generation station 15receives hot exhaust gas from the furnace 300 and uses heat from thefurnace exhaust to generate steam. The boiler 302 includes a pluralityof steam tubes 330 that extend from a mud drum 332 to a steam drum 334.Steam from the steam drum 334 is super heated at a superheater 336. Heatof combustion from the furnace 300 is utilized to evaporate water in thesteam tubes 330 such that steam is provided to the steam drum 334, andis also used to superheat the steam in the superheater 336. As shown atFIG. 14, hot exhaust output from the furnace 300 flows into the boiler300. In the boiler, the exhaust gas initially flows across thesuperheater 336 and then flows across the steam tubes 330. Superheatedsteam from the superheater 336 is conveyed to the steam turbinegenerator 17. Specifically, the superheated steam is directed to thesteam turbine 303 which powers the electrical generator 305. Afterpassing through the steam turbine 303, the steam is passed through acondenser (e.g., cooling towers) and then routed in a closed path backthrough a deaerator and a heat exchanger 338 to the mud drum 332. Theheat exchanger 338 uses heat in the furnace exhaust gas exiting theboiler 302 to preheat the feed water before the feed water enters themud drum 332. Make-up water can be fed into the closed system throughthe deaerator. The make-up water is preferably routed through apurification system prior to entry into the closed system.

In certain embodiments, the boiler is capable of continuously generating190,000 pounds per hour to 220,000 pounds per hour of steam whileoperating at a pressure of 900 pounds per square inch gauge (psig) atthe superheater outlet and a temperature of 900 degrees Fahrenheit steamtemperature at the superheater outlet. In certain embodiments, theboiler is operated at a pressure of 800-1,000 psig, or 850-950 psig, oraround 900 psig at the superheater outlet. Also, in certain embodiments,the output steam from the superheater outlet has a temperature of800-1,000 degrees Fahrenheit, or 850-950 degrees Fahrenheit, or about900 degrees Fahrenheit.

Corn residue has relatively high concentrations of alkali andalkaline-earth elements (e.g., potassium, phosphorous, sodium,magnesium, and calcium). Corn residue also has a high concentration ofamorphous silica. This provides an increased potential for a high degreeof ash deposition within the boiler (e.g., on the boiler tubes,superheater and other structures of the boiler). Deposition layersformed on the components of the boiler insulate the boiler componentsthereby negatively affecting the heat transfer efficiency of the boiler.Ash deposition rates are dependent upon exhaust temperature. In thisregard, it has been determined that ash deposition rates resulting fromthe combustion of corn residue are manageable if the furnace 300 isoperated such that the furnace 300 target furnace exit gas temperature(FEGT) is preferably less than 1800 degrees Fahrenheit, and morepreferably less than 1700 degrees Fahrenheit. The FEGT is thetemperature of furnace exhaust gas which exits the furnace 300 through afurnace outlet 340 and enters the boiler 302. In certain embodiments,the FEGT is in the range of 1,400 to 1,800 degrees Fahrenheit. In apreferred embodiment, the FEGT is in the range of 1,400 to 1,700 degreesFahrenheit. Soot blowers can also be used to help remove ash deposits.

Upon exiting the boiler 302, the furnace exhaust gas can pass throughthe heat exchanger 310 to preheat the combustion air being fed into thefurnace 300 below the stoker grate 304. From the heat exchanger 310, theexhaust gas passes through an ash removal component 342. In a preferredembodiment, the ash removal component includes a cyclonic particulateseparator that removes ash from the exhaust gas stream by centrifugalaction and discharges the ash through an ash outlet 343. The exhaust gasexits the particulate removal component 342 at an exhaust outlet andpasses through the heat exchanger 338 where heat from the exhaust gas isused to preheat the feed water being routed from the condenser throughthe deaerator to the mud drum 332. An acid treatment station 347 isprovided downstream from the heat exchanger 338 for neutralizing acid(e.g., hydrochloric acid) in the exhaust stream by the addition of abase material (e.g., sodium bicarbonate). An induced flow fan 344 ispositioned downstream from the acid treatment station 347 for pullingthe exhaust flow through the system such that a slight vacuum isprovided at the furnace 300.

Downstream from the fan 344 is a re-circulated air access location 346where a portion of the exhaust gas is diverted from the exhaust streamand re-circulated back to the furnace 300. As shown in the depictedembodiment, the diverted exhaust gas can be directed to the pneumaticfuel distribution system 320. In this way, the recirculated air isinjected into the furnace 300 above the stoker grate as part of the fueldelivery process. The diverted exhaust gas can also be injected into thefurnace 300 through the nozzles 314 provided at the upper combustionregion 312. A precipitator 348 is downstream from the re-circulated airaccess location 346. The precipitator 348 functions to precipitate flyash as well as material neutralized at the acid treatment station 346.The precipitated material is collected in hoppers. A conveyor can beused to move the ash collected at the particulate removal component 342and the precipitate material collected at the precipitator to an ashcollection silo 350. From the precipitator 348, the exhaust can bedirected to an outlet stack 356

It has been determined that the ash has considerable nutrient value thatmakes it suitable for use as a fertilizer. The primary constituent ofthe ash includes a silica based compound (e.g., SIO₂). Silica basedcompounds typically constitute over 30% of the ash. Additionally,potassium based compounds (e.g., K₂O) can constitute at least 30% of theash, phosphorus based compounds (e.g., PTO₅) can constitute at least 5%of the ash and carbon based compounds can constitute at least 5% of theash. Other chemicals present in the ash include Al₂O₃, Fe₂O₃, TiO₂, CaO,MgO and Na₂O. In certain embodiments, the collected fly ash is conveyedto a pelletizer 352 (e.g. pelletizing mill) where the ash is compactedinto pellets. The pellets can be sold in bulk or bagged and sold asfertilizer or soil additive.

It is also possible to co-fire the above-ground corn residue in thefurnace 302 with a secondary fuel source. For example, FIG. 14 shows anoptional secondary fuel source 360 for delivering a secondary fuel tothe fuel metering arrangement 322. Preferably, the above-ground cornresidue remains the primary fuel source with a smaller amount of thesecondary fuel being mixed with the above-ground corn residue. Incertain embodiments, the secondary fuel has a higher BTU value than theabove-ground corn stover. An example of a higher BTU value secondaryfuel comprises excess or waste seed (e.g., corn seed, soybean seed,etc.) from a seed company. In certain embodiments, the waste seed can bechemically treated seed that has been treated with a pesticide, afungicide or another type of chemical treatment. The blended fuelresulting from the mixture of corn stover with the secondary fuelpreferably has an average piece length less than 3 inches with no morethan 25 percent by weight being less than 0.25 inches in length. Incertain embodiments, the blended fuel mixture has a compositionincluding at least 75 percent by weight that is less than 3 inches inlength and no more than 25 percent by weight that is less than 0.25inches in length.

The above specification provides examples of how certain aspects may beput into practice. It will be appreciated that the aspects can bepracticed in other ways than those specifically shown and describedherein without departing from the spirit and scope of the presentdisclosure.

What is claimed is:
 1. A method for combusting corn stover to produceheat for generating steam, the method comprising: combusting the cornstover in a furnace to produce heat; using the heat from the combustionin the furnace to generate steam in a boiler; operating the furnace suchthat the furnace has an outlet exhaust gas temperature in the range of1400 degrees F. to 1800 degrees F. so as to reduce ash deposition withinstructures of the boiler; operating the furnace and the boiler such thatthe boiler provides a steam pressure in the range of 800-1000 psig at asuperheater outlet; operating the furnace and the boiler such that theboiler provides a steam temperature in the range of 800-1000 degrees F.at the superheater outlet; and operating the furnace and the boiler tocontinuously generate 190,000 pounds to 220,000 pounds of steam perhour.